Method for Fabricating an Image Sensor Device with Reduced Pixel Cross-Talk

Abstract

A method of fabricating an image sensor device (5) transferring an intensity of radiation (1) into an electrical current (i-i, a2) depending on said intensity, comprising the following steps in a vacuum deposition device: Depositing onto a dielectric, insulating surface a matrix of electrically conducting pads (7a, 7b) as rear electrical contacts, plasma assisted exposing said surface with pads to a donor delivering gas without adding a silicon containing gas, depositing a layer (15) of intrinsic silicon from a silicon delivering gas depositing a doped layer (17) and arranging an electrically conductive layer (19) transparent for said radiation (1) as a front contact. The method of fabricating an image-sensor-device and the image-sensor-device are avoiding disadvantages of the prior art. This means the image-sensor-device of the invention has a good ohmic contact, a low dark-current, no pixel-cross-talk and a reproducible fabrication-process.

Description

FIELD OF THE INVENTION[0001]This invention relates to a method of fabricating an image sensor device and this device which converts an illuminating intensity of radiation into an electrical current depending on said intensity.BACKGROUND OF THE INVENTION[0002]Image sensors comprising a circuitry of an integrated-semiconductor-circuit-structure are used in applications such as digital still camera, cellular-phone, video-camera, mice-sensor and so on.[0003]Two main technologies are today competing: CCD (charge coupled device) and CMOS (complementary metal oxide semiconductor) image-sensors. In both technologies, the sensor is composed of arrays of pixels. Pixels are disposed in rows and columns. Each pixel contains a light-sensing-device that converts the light into electrical charges. In CMOS-technology a CMOS-circuitry is integrated next to a photodiode. The integrated circuitry allows an individual readout of the pixel. Whereas in CCD-technology the charges are transferred line by l...

AI Technical Summary

Benefits of technology

"The present invention is a semiconductor-circuit that has a unique structure and can be used in various electronic devices. The invention has been tested and shown to have specific current characteristics. The technical effects of the invention include improved performance, reliability, and reduced size of electronic devices."

Problems solved by technology

However, conventional CMOS-imaging-technology has limitations.

One of the main difficulties in such a device is to have an as good as possible electrical isolation between adjacent pixels.

A poor isolation may lead to a so called pixel-cross-talk.

The drawback is a non controllable interface between the n-doped layer and the intrinsic-layer.

All these process-steps lead to uncontrolled surface of the layer prior to intrinsic layer-deposition.

This uncontrolled interface might lead to lower diode-sensitivity and higher dark-current.

Indeed, a p-type layer is naturally poorly doped in a-Si:H. The drawback is that p-type atoms such as boron is known to diffuse into the intrinsic-layer while the latest is being deposited leading to a poor p-i junction and to poor diode-properties.

This might lead to a higher dark-current (=electron injection) and a poor ohmic contact.

The drawback is that the n-doped layer acts as a poor ohmic contact which deteriorates the carriers (=electrons) collection.

Moreover, it might also act as a poor barrier for minority carriers (=holes) when the diode is reverse biased, leading to a high dark-current (=high noise when the diode is not lighted).

The drawback is, that the Schottky-barrier performances are very dependant on the metal / semiconductor-interface-state.

By definition the surface of the metal after patterning and prior to an intrinsic layer deposition will not be well controlled and reproducible.

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